This invention relates to a honeycomb structure used as a substrate for catalysts for purifying exhaust gases from internal combustion engines, as a filter for removing fine particles in exhaust gases, and as a substrate for various catalysts for deodorizing and/or purifying burnt gases when fuels such as various gases or petroleum are burnt, and more particularly to a method of producing such a honeycomb structure.
FIG. 1 illustrates a catalyst converter which has been generally practically used for purifying exhaust gases from an automobile loaded with the converter. In order to make the converter insusceptible to violent vibrations in use, it comprises cushion members 22-1 and 22-2 and sealing members 22-3 about a honeycomb structure having through-apertures 21-1 through which exhaust gases pass and plate members 23 on upstream and downstream sides of the structure. The cushion members and the sealing members apply forces upon the honeycomb structure in traverse or lateral directions (referred to as "radial directions" hereinafter) of the directions of the through-apertures 21-1 and the plate members 23 apply forces directly or through the cushion members 22-1 onto the honeycomb structure in the directions of the through-apertures 21-1. The honeycomb structure is fixed and held thereat in this manner.
With such a construction of the catalyst converter, however, the cushion members 22-1 or the plate members 23 close some apertures 21-2 of the through-apertures 21-1 so that exhaust gases do not pass through the apertures 21-2, with the result that the catalyst carried by the portions of the apertures 21-2 will be inoperative.
In order to avoid this disadvantage, it has been practically proposed to hold a honeycomb structure in radial directions by seal members arranged radially outward of the honeycomb structure for the purpose of saving catalytic noble metals. Moreover, a honeycomb structure has been known which is formed on its outer circumference with barriers adjacent at least one end face of a sealing member as disclosed in Japanese Utility Model Application Laid-open No. 62-179,319.
With the limitedly practically used honeycomb structure being only radially supported, however, high pressure is required to radially support the structure in order to fix it against movement caused by violent vibrations generated in use. It is possible to support it radially in case that thicknesses of partition walls of the ceramic honeycomb structure are comparatively thick, for example, 0.30 mm to provide a high strength against external pressures. However, such a supporting of the honeycomb structure is not applicable to a honeycomb structure whose partition walls are relatively thin such as 0.15 mm to 0.20 mm and susceptible to external pressures.
In the honeycomb structure disclosed in the Japanese Utility Model Application Laid-open No. 62-179,319, however, partition walls are formed separately from a main body of the honeycomb structure, so that there is a difficulty in adhesiveness therebetween. In more detail, even if a thermosetting inorganic filler consists mainly of a ceramic material such as alumina, silica and the like, it encounters a problem of peeling or separation in the case that a material of the honeycomb structure is cordierite, which is widely used. Such peeling results from thermal shocks which are repeatedly generated in use because of the larger thermal expansion of the filler than that of the honeycomb structure itself.
Therefore, although the high adhesiveness can effectively prevent the members of the structure from being shifted in directions of through-apertures of the structure without increasing the holding force, if the adhesiveness becomes less, it cannot prevent the shifting of the members in the directions of the through-apertures.
The barriers provided on the outer circumference of the structure are effective to prevent the shifting of the members in axial directions, but they do not serve to prevent shifting in radial directions or rotation of the members.